The present invention relates to an anti-blur infrared lens for a panoramic camera system using HD resolution sensor. To be specific, the anti-blur infrared lens for the panoramic camera system using the HD resolution sensor mentioned in the invention is applied in electro-optical systems, thermal imaging systems for search and surveillance applications on civilian and military equipment.
Along with the development of infrared imaging technology, the demand for optical systems using high-quality thermal images is increasing dramatically. The ability to observe in extreme environmental conditions with limited visibility such as night time or environments with smoke, dust, and fog makes infrared lenses, especially ones operate in the mid-wave infrared spectral region, play an extremely important role and indispensable component in search and surveillance systems in the military as well as civilian applications.
Infrared lenses with anti-blur capabilities has become an integral component in panoramic surveillance electro-optical systems, giving these systems good visibility in both stationary mode and continuous scanning mode.
Recently, there have been many inventions of optical systems at mid-infrared wavelengths used for surveillance systems, especially the IRST panoramic camera system. Most of these inventions meet the requirements of technical specifications, structure and image quality, yet there are still many limitations in terms of applicability. Specifically, in U.S. Pat. No. 9,482,853, the design uses three large asymmetrical mirrors to create the magnification of the lens. This makes manufacturing and assembling difficult because the position of the mirrors requires extremely high accuracy. In another patent, U.S. Ser. No. 10/690,903, a design uses up to fifteen lens elements and one prism element to accommodate image blur compensation. However, with a large number of elements, it leads to the low transmission, reducing the visibility of the device. In another invention of this type of lens, the optical structure is compatible with a 1280×720 resolution sensor, but the field of view per frame is only less than 3° in each direction, making the viewing angle of the device small and unsuitable for a panoramic surveillance device. Another drawback of this invention is that the maximum compensation angle of the mirror is only 1.2°, making it difficult for the surveillance system to achieve the desired high updating speed.
From these information, coupling with the knowledge and experience in designing optical lenses, the authors propose an anti-blur infrared lens for the IRST panoramic camera system using the HD resolution sensor. This invention meets the rigorous requirements in terms of the specifications, while also solving the above mentioned limitations. Specifically, the lens is designed with a folding structure that uses a scanning mirror to compensate for the line-of-sight of the device when the camera module is acquiring images, ensuring image stability. This lens has a per-frame field of view of up to 10°×8° and is capable of responding to mirror compensation angles of up to 2° with a system update frequency of up to 360°/s. In addition, the lens uses a second folding mirror to ensure the layout space of the sensor inside the size of the lens, providing compactness for the design. In this invention, a pair of lenses with extended polynomial surfaces are simulated, calculated and selected to be used to reduce the effect of image wander with the greatest efficiency, so that the image quality is maintained throughout the exposure time of the sensor. Image wander is the phenomenon in which the image of the fields in the boundary region are moved when the system is scanning and the mirror changes the flip angle; Although the image centre area is kept fixed on the image plane, the image positions in the boundary area are changed causing the image quality to deteriorate during the scanning process. This phenomenon becomes more severe and causes more blurriness as the device rotation speed and field of view per frame increase.
The above problem has been minimized almost completely with the successful research and design of an infrared anti-blur lens for the IRST panoramic camera system using an HD resolution sensor, specifically a cooling sensor with a working F-number of 2, a resolution of 1280×1024 pixels and a pixel pitch of 15 μm.
The purpose of the present invention is to propose an anti-blur thermal imaging lens for camera scanning systems using HD resolution sensor with a large aperture. The structure of the lens from the object plane to the image plane consists of five main groups, therein:
An external lens group (G1) consists of six lens elements with the task of receiving an incident parallel beam, creating an image in the intermediate plane, and transforming the outgoing beam to be afocal with a fixed magnification.
A fast steering mirror group (M1) stabilizes the direction of light rays after reflecting through the mirror.
A converging lens group (G2) creates a second intermediate image.
A second fixed mirror group (M2) changes the direction of the beam at an angle of 45°, making the lens structure compact.
An intermediate magnification group (G3) magnifies the image from the intermediate image to the sensor.
The folding structure of the lens is achieved by using two reflectors with an average reflectance ratio in the wavelength range of approximately 98%. The first mirror is a fast steering mirror used to help the lens maintain the line-of-sight as the device scans. The second mirror makes it possible for the cooling sensor to be compactly arranged, making the lens housing size smaller.
According to this structure, the ratio of the focal length of the whole lens to the focal length of the imager group is exactly equal to the magnification ratio of the afocal magnifier according to the calculation f(lens)=f(imager group)×magnification ratio.
According to this structure, the magnifying lens group has the effect of magnifying the angle of the light beam into the lens while preserving the “afocal” nature of the outgoing light beam.
According to this structure, the lens uses a fast steering mirror to maintain the line-of-sight of the device. The lens is optimized to accommodate an angle of change up to 2° at a scanning speed of 360°/s, ensuring that during the operation, the image sharpness is maintained in scanning mode or rest mode.
According to this structure, the displacement of lens 8 is used for active focus and thermal compensation in the temperature range of −20÷65° C. and focusing distance from 20 m to infinity.
According to this structure, the lens uses a group of two lenses 3 and 4 with extended polynomial surfaces, making the lens resistant to image blur when the device is scanning at high speed.
According to this structure, the distance from the exit pupil of the lens to the sensor and the diameter of the exit pupil are set to match the parameters of common commercial high-definition detectors on the market. To ensure that the lens is compatible with cooling sensors with a working F-number of 2, the ratio between the distance from the exit pupil of the lens to the sensor and the diameter of the exit pupil is less than 2.
The lens design uses several aspheric surfaces and hybrid aspherical-diffractive surfaces to increase optical quality, reducing the total number of elements required in the lens design.
According to this structure, the anti-blur infrared lens for the IRST panoramic camera system uses an HD resolution sensor to collect infrared radiations within the wavelength range of 3-5 μm and focus on the sensor with a resolution of 1280×1024 and a working F-number of 2, creating clear images in every field of view of the device and at any compensation angle of the mirror in the field of view.
The invention of an anti-blur infrared lens for an anti-blur scanning system using an HD resolution sensor whose structure is illustrated in
Referring to
According to this structure, the group (G1) has the effect of magnifying the focal length of the optical part created by the group (G2, G3) to a certain magnification ratio (A). In order to ensure the magnification of the group (G1), the focal ratio f(L1,L2,L3)/f(L4,L5,L6)=A. In addition, the magnification ratio is between 1.2 and 2.0 therefore 1.2≤f(L1,L2,L3)/f(L4,L5,L6)=A≤2.0.
Referring to
In conformity with this structure, referring to
In which α is the rotation angle of the mirror, β is the rotation angle of the device in the integration time for each frame, A is the magnification ratio of the group (G1).
Referring to
Referring to
Referring to
Referring to
1.1≤f(G1,G2,G3)/f(G1,G2)≤2.5
In which:
f(G1,G2,G3) is the focal length of an optical part formed by groups G1,G2,G3;
f(G1,G2) is the focal length of the optical part formed by groups G1,G2.
Referring to
Referring to
Referring to
Referring to
According to this structure, the invention of an anti-blur infrared lens for a panoramic camera system using an HD resolution sensor is designed to satisfy the following conditions:
In which:
f(L1,L2,L3) is the focal length of the optical part formed by the lenses (L1), (L2), (L3);
f(L4,L5,L6) is the focal length of the optical part formed by the lenses (L4), (L5), (L6);
f(G1,G2,G3) is the focal length of the optical part formed groups (G1), (G2), (G3);
f(G1,G2) is the focal length of the optical part formed by the groups (G1), (G2);
β is the rotation angle of the device each time it takes one frame;
d is the distance from exit pupil to image plane;
D is the diameter of the exit pupil of the lens.
An example is made for the invention of an anti-blur infrared lens for a panoramic camera system using an HD resolution sensor 1280×1024 F/#2 sensors, with detailed parameters are as follows:
The unit of measure used in the tables is ‘mm’
The aspherical surfaces are defined by the following formula:
In which:
R is the radius of curvature of the aspherical surface
y is the axial height from the optical axis
k is the conic constant of the aspherical surface
A2i are respectively the even order aspherical coefficients of 2, 4, 6, 8,10, 12, . . .
The table below lists the aspherical parameters of some lens surfaces:
The diffractive surfaces used in the design are described by the following polynomial expansion:
In which:
Φ is the phase added to the ray at the coordinates defined by ρ,
Ai are the coefficients of the polynomial that are optimized during the design process.
ρ là the normalized coordinate at the diffractive surface.
The table below lists the diffraction coefficients at the S14 and S20 surfaces:
The extended polynomial surfaces are defined by the following polynomial:
In which:
z is the sag at the calculated point
k is the conic constant of the surface
c is the curvature of the surface
r is the radius at coordinates x,y
N is the number of coefficients of the polynomial
Ai is the coefficient corresponding to the monomial of order i
Ei(x,y) is the monomial of x and y corresponding to order i
The following table lists the coefficients corresponding to the respective monomials of the surfaces S6 and S7:
The detailed description of this invention has been specifically explained above, however it should also be understood that the descriptions presented are merely a model of the invention, it can be expressed in many different forms. Therefore, the details of the parameters presented here should not be considered as a limitation, they are only the basis for other proposals.
Number | Date | Country | Kind |
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1-2021-07679 | Nov 2021 | VN | national |